Rotor blade and shroud assembly



Nov. 27, 1962 F. HARLTIN 3,065,955

' ROTOR BLADE AND SHROUD ASSEMBLY Filed Dec. 29, 1958 INVENTOR. FZ 0V0#461 M/ United States Patent 3,065,955 ROTOR BLADE AND SHROUD ASSEMBLYFloyd Harlin, Cincinnati, Ohio, assignor to General Electric Company, acorporation or New York Filed Dec. 29, 1958, Ser. No. 783,487 1 Claim.(Cl. 253-7 7) This invention relates to gas turbine type engines andmore particularly to rotor blade and shroud assemblies for axial flowcompressors and the like for gas turbine type engines.

One of the problems inherent in the use of axial flow compressors is thesubjection of rotor blades to flexural and torsional vibrationalstresses. Various arrangements have been provided in the prior art whichattempt to solve this problem. For example, some of the prior artprovides shrouds surrounding rotor blade tips for the purpose ofminimizing vibrational stresses. Other solutions include disclosureswherein blade tips are slotted to receive tongues depending from thecylindrical shroud members. However, one of the prime requirements inmodern high speed gas turbine design is a light-weight structure capableof eflicicnt operation at high rotational speeds. The prior art of whichI am aware has failed to provide a structure that is light-weight andcapable of minimizing vibrational stresses. By the use of my invention,lightweight shrouding may be employed having great strength and capableof minimizing vibrational stresses. While I discuss the invention inconnection with compressors, it will be obvious that it is alsoapplicable to turbines and the term compressor is merely used forillustration.

Accordingly, it is an object of this invention to provide an improvedcompressor rotor blade and shroud assembly which has a highstrength-to-weight ratio and is capable of use at high rotationalspeeds.

Another object of this invention is to provide an improved rotor bladeand shroud assembly capable of minimizing the fiexural and torsionalvibrational stresses present in the lightweight rotor blades.

A third object of this invention is to provide an improved rotor bladeand shroud assembly having means to minimize bending stresses resultingfrom high centrifugal loads acting upon the shroud.

A further object of this invention is to provide an improved rotor bladeand shroud assembly having means to minimize aerodynamic gaps andprovide a smooth flow path.

These and other objects and advantages of this invention will becomemore apparent as the following description proceeds.

Briefly stated, in accordance with one embodiment of my invention, Iprovide a compressor rotor blade shroud composed of a plurality ofarcuate segments which are secured to the tips of rotor blades and, whenassembled, form a substantially annular shroud. Each shroud segment hasa plurality of outwardly extending, circumferential ribs which providestrength, minimize bending stresses, and provide openings positioned toreceive blade securing means. A plurality of radial slots are located ineach shroud segment and these slots receive outwardly extending tangs onthe blade tips. These tangs have openings which align with the openingsin the outwardly extending ribs, and which are positioned to receive apin or similar means to secure the shroud to the blade tips. The shroudstructure is located within grooves formed within the stator casing, andthe shroud has substantially axially extending overhanging projectionswhich cooperate with the stator casing to form a smooth flow path.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which I regard as myinvention, it is believed that the invention will be better understoodfrom the following "ice description taken in conjunction with theaccompanying drawing in which:

FIG. 1 is a plan view of a portion of a shroud segment;

FIG. 2 is a cross-sectional view taken on line 2-2 of FIG. 1 showing theshroud and blade assembly; and,

FIG. 3 is a perspective view of a portion of a rotor blade showing thetang arrangement.

Referring to FIGS. 1 and 2, a light-weight compressor rotor blade andshroud assembly has been illustrated. In this arrangement, only onestage of rotor blades has been shown for the purpose of simplicity andclarity. However, it will be understood that the following descriptionrelating to this stage is equally applicable to each stage of bladesused. The shroud and blade assembly includes a plurality of arcuatesegmental shroud members, one of which is shown at 1 transversely andperipherally spanning the ends of the blades, and a plurality oflight-weight'r'otor blades, one of which is shown at 2, which aremounted within a stator casing 3.

In order'to accomplish the dual functions of strengthening the rotorassembly while maintaining a high strengthto-weight ratio, and also ofproviding for the joining of the blades and the arcuate'shroud members,the shroud members are formed to provide a base member and to include aplurality of spaced circumferential ribs extending outwardly therefrom.In the preferred embodiment of my invention, three ribs 4, 5 and 6 havebeen employed. The ribs have a plurality of aligned openings 7. Aplurality of tang receiving radial slots 8 and 9 are formed in theshroud members 1 between the spaced outwardly extending ribs. The use ofoutwardly extending ribs provides a shroud of relatively light weight,yet having high strength characteristics. In carrying out my inventionin practice, I have found the following dimen sions of the shroudstructure to be satisfactory; as for example, when used with a shroudsegment of 45 degrees in arc and having a base of .05 inch or less inthickness on a blade of 1.5 inches chord, the ribs are .05 to .0 8 inchthick and .25 inch high. It will, of course, be understood that thesedimensions are given by way of example only and that the dimensions willhave to be varied in accordance with the many variables encountered indifferent gas turbine designs.

A compressor rotor blade 2 having a working fluid face 10 and outwardlyextending tangs 11 and 12 is shown in FIG. 3. The tangs have openings 13positioned to align with the openings 7 in the shroud ribs. Uponassembly, the blade tangs 11 and 12 are inserted through radial slots 8and 9 and between ribs 4 and 5, and 5 and 6, respectively. A locking pin14 is inserted in aligned openings 7 and 13 to secure the shroudtransversely .and peripherally spanning the ends of the light-weightrotor blades.

In FIG. 2 the stator casing is shown provided with first and secondoutwardly directed but inwardly facing internal circumferential steppedshallow and deep grooves 15 and 16 respectively, which are positioned toreceive the blade and shroud assembly with 15 being wider than 16. Thearcuate, segmental shroud members 1 are provided with substantiallyaxially extending, upstream and downstream projections 17 and 18. Theprojections are entirely received within and span radially inner groove15 .and thereby establish a smooth flow path through the casing. Theprojections also form substantially annular members, the outer surfacesof which are positioned in close proximity to the substantiallycylindrical inner surfaces of groove 15, thus providing a radial seal tominimize the leakage of fluid between the shroud and the casing.Circumferential groove 16 is positioned to receive the outwardlyextending ribs 4, 5 and 6, and tangs 11 and 12.

Thus it may be seen that a plurality of blade tips are securely tiedtogether by means of compressor rotor shrouds. In addition to reducingfiexural and torsional vibrational stresses in the light-weight rotorblades, the shroud further serves to provide a smooth flow path and toprovide a radial seal between the shroud and the casing.

It is obvious that I have provided a simple, light-weight shroudassembly capable of being used in modern high speed applications. Theribs 4, 5 and 6, in addition to providing receiving means for the bladelocking pins, also serve to minimize bending stresses imposed by highcentrifugal loads acting upon the shroud between blade tips. Further,the ribbed structure provides for a high strength-to-weight ratio notheretofore possible when using known prior art structures. Additionally,the substantially axial shroud projections serve the dual functions ofinsuring a smooth fiow path and providing a radial seal.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects and I, therefore, aim in the appendedclaim to cover all such changes and modifications as fall within thetrue spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

A shrouded rotor assembly comprising:

(a) a plurality of blades mounted on said rotor,

(12) a segmental arcuate shroud member transversely and peripherallyspanning the ends of said blades and secured thereto,

(c) a stator casing enclosing said blades,

(d) a circumferential groove in said casing having a deep centralportion and a shallow portion wider than the deep portion extendingaxially from each side of said deep portion and terminating at the innersurface of said casing,

(e) a radially protruding circumferential portion on said shroudextending into said deep central portion of said groove, and

(f) one axial projection on each side of said circumferential portionextending into respective parts of the shallow portion of said groove toform a smooth flow path through the casing and a radial seal betweensaid shroud and said casing.

References Cited in the file of this patent UNITED STATES PATENTS764,451 Geisenhonor July 5, 1904 903,167 Boyd Nov. 10, 1908 906,400Ferranti Dec. 8, 1908 980,562 Rice Jan. 3, 1911 1,158,755 Weaver Nov. 2,1915 1,371,328 Schneider Mar. 15, 1921 1,457,404 Snyder June 5, 19.231,876,067 Lorenzen Sept. 6, 1932 1,998,951 Downer Apr. 23, 19352,518,660 Browne Aug. 15, 1960 2,959,893 Rankin Nov. 8, 1960 FOREIGNPATENTS 342,900 Germany Oct. 26, 1921

